The causes of most human mental retardation and neurological defects remain unknown. We propose to use teratological, biochemical, and immunological approaches to determine whether defects in selected molecular and cellular components result in gross abnormalities of the nervous system and related tissues. An evaluation will be made of the role of contractile elements (actin, myosin and related proteins) in motile processes essential to normal neural development. Antibodies to these components will be used in efforts to experimentally produce neural defects in chicks and mice. Likewise, the role of specific neural cell surface antigens in brain organogenesis will be examined and efforts to experimentally induce neural defects with antibodies to these components initiated. Human amniotic fluid and serum samples will be tested for antibodies to cytoskeletal proteins and neural specific cell surface antigens. In another approach, the presence and role of neural crest cells in the morphogenetic movement of mouse palate will be examined. Factors influencing the migration of neural crest cells will be tested. The effects of chemical teratogens on cultured neural crest and non-neural cells will be examined to determine if neural cells are particularly sensitive to these agents. The combined analysis of these molecular and cellular aspects of neural development should lead to more rational approaches to the etiologies of human mental retardation.